Athlete burnout is conceptualized as an enduring multidimensional syndrome, and longitudinal research is essential to understanding its development over time. However, much of the existing work has been limited to a small number of timepoints (≤3) or short intervals between waves (≤3 weeks), which fail to account for the chronic and complex nature of the syndrome. This study aimed to address these limitations by tracking burnout in adult athletes at 6 timepoints over a 21-month period for the first time. Data from 207 Gaelic games athletes were included in latent growth analysis to compare burnout trajectories of increasing complexity. A linear model best described all burnout symptoms. On average over the 21-month period, feelings of exhaustion declined, sport devaluation increased, and reduced accomplishment remained stable. Findings provide important insight into potential high-risk periods in the season and can help to inform targeted intervention or prevention efforts.